[Add] cosyvoice object pool, support set url, workspace and headers (#75)

Author: lengjiayi

dashscope/audio/tts_v2/__init__.py

@@ -1,9 +1,12 @@
 # Copyright (c) Alibaba, Inc. and its affiliates.
 
 from .enrollment import VoiceEnrollmentException, VoiceEnrollmentService
-from .speech_synthesizer import AudioFormat, ResultCallback, SpeechSynthesizer
+from .speech_synthesizer import (AudioFormat, ResultCallback,
+                                 SpeechSynthesizer,
+                                 SpeechSynthesizerObjectPool)
 
 __all__ = [
     'SpeechSynthesizer', 'ResultCallback', 'AudioFormat',
-    'VoiceEnrollmentException', 'VoiceEnrollmentService'
+    'VoiceEnrollmentException', 'VoiceEnrollmentService',
+    'SpeechSynthesizerObjectPool'
 ]